Field of the Invention
The present invention relates to a capacitor mounted on a surface acoustic wave (SAW) filter, the SAW filter including the capacitor, and a method of manufacturing thereof.
Background of the Related Art
A surface acoustic wave (SAW) filter is a device for transferring signals using surface acoustic waves having physical characteristics, not electromagnetic waves, and removing unnecessary signals in the process of transferring the signals. The SAW filter is used for video signal processing or audio signal processing of a TV, a VTR or the like, and as mobile communication is advanced recently, it is widely used for mobile communication terminals. SAW duplexing of dielectric duplexers is under progress according to miniaturization and lightweightness of the mobile communication terminals, and miniaturization of the SAW filter using a flip-chip process is under progress.
On the other hand, a capacitor is an important device for storing information in DRAM or embedded DRAM, which are memory elements, an RF ID element which is a logic element, or the like. In the memory element, the capacitor stores electric charge of a predetermined amount or more inside thereof to distinguish 0 and 1 to make operation of a desired device possible. In the semiconductor industry, it is very important to develop a technique of manufacturing an ultrahigh density element integrated under a 50 nano size to simultaneously implement cost reduction, low power consumption and miniaturization of a chip, and to this end, a technique of allowing a capacitor, which stores data, to have a capacitance sufficient for operating a device is more important than any other techniques.
FIG. 1A is a plan view schematically showing an Inter-Digital Transducer (IDT) and a capacitor applied to a SAW filter of the prior art, and FIG. 1B is a cross-sectional view schematically showing a capacitor applied to a SAW filter of the prior art. Referring to FIGS. 1A and 1B, in a SAW filter, an upper electrode 23 and a lower electrode 21 is generally formed of poly-crystal silicon (poly-Si), and a capacitor 20 having a dielectric substance 22 formed between the upper electrode 23 and the lower electrode 21 is applied. However, since it is difficult to obtain a desired capacitance of a cell as the area of the cell decreases, a capacitor 20 replacing the upper electrode 23 with a metallic electrode of TiN or the like to prevent a low dielectric layer from being formed between the upper electrode 23 and the dielectric substance 22 and applying a dielectric film such as Al3O3, Ta2O5 or the like to have a dielectric substance 22 of high permittivity is commercialized and applied.
FIG. 2A is a plan view schematically showing an IDT and another capacitor applied to a SAW filter of the prior art, and FIG. 2B is a cross-sectional view schematically showing another capacitor applied to a SAW filter of the prior art. Referring to FIGS. 2A and 2B, an IDT capacitor 30 is applied to a SAW filter in which an IDT 10 is formed. The IDT capacitor 30 is formed by stacking a first metal layer 32 formed by using a metal the same as that of an electrode 10 on a substrate 31.
However, there is a problem in that the duplexer SAW filter applied with such conventional capacitors 20 and 30 of the prior art cannot have an ideal low cut-off characteristic.